Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
709 PM EDT Wed Aug 11 2021
Valid 12Z Sun Aug 15 2021 - 12Z Thu Aug 19 2021
...Overview...
An upper low will remain/meander in the Arctic/Beaufort through
next week with systems moving eastward underneath its circulation
across northern areas. Additional troughing will reload near the
Aleutians into the Gulf to the north of building upper ridging in
the mid-latitudes. This keeps a quasi-zonal flow across much of
the mainland into the Panhandle with several systems and rainfall
episodes.
...Guidance/Predictability Evaluation...
The ensembles remained in good agreement overall with some
expected timing/amplitude differences next week over the Bering
and near the Aleutians as a couple more systems enter the picture.
Overall, a blended solution was preferred. This included the 12Z
ECMWF which paired best with the ensembles, followed by the 12Z
GFS and Canadian. The UKMET was again farthest from the consensus.
The lead systems south of the Aleutians Saturday, containing the
remnant moisture of ex-Tropical Storms Lupit and Mirinae, will
tend to lift northeastward toward the central/eastern Aleutians
and AKPen next week, bringing in some rainfall to the region. The
system will move into the Gulf around late next Tue with a middle
ground solution showing little change from the forecast 24 hrs
ago.
...Weather/Threats Highlights...
Over northwestern areas, deep upper low in the Arctic will allow a
northern stream system out of Russia to push eastward
underneath/around its circulation. This will bring in an expanding
area of precipitation to the northwestern corner of the state and
across the Brooks Range early next week as the boundary slowly
sinks southward and then eastward just ahead of the upper trough.
Some rainfall could be locally modest to heavy over the Seward
Peninsula eastward to the Koyukuk and Yukon River Valleys. By
later next week, system will move through the Gulf bringing
another round of rain for the Panhandle.
Temperatures will generally be below normal across most of the
state, focused on northern areas under the trough. Some slow
moderation is possible later next week but the continued troughing
will likely result in only small changes to the pattern, perhaps
nearing or above normal temperature across the Aleutians by next
Wednesday/Thursday.
Fracasso
Additional 3-7 Day Hazard Information can be found on the WPC
medium range hazards outlook chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php
Hazards:
- Heavy rain across portions of mainland Alaska, Sun-Mon, Aug
15-Aug 16.
- Heavy rain across portions of the Alaska Panhandle and mainland
Alaska, Tue-Wed, Aug 17-Aug 18.
WPC medium range Alaskan products including 500mb, surface
fronts/pressures progs and sensible weather grids can also be
found at:
https://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml
https://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html